U.S. Patent No. 5,122,039 discloses a gerotor-type fuel pump that internally carries an elastomeric pressure pulse damper containing air at atmospheric pressure within a closed hollow and circumferentially continuous annular body which functions to reduce pressure pulsations in the fuel output to enhance pump delivery and reduce audible noise. Fuel is pumped by the action of a pair of intermeshing inner and outer gear rotors positioned within a housing which produce pressure pulses or variations in the pressure of the fuel discharged from the pump. The pressure pulse damper contracts and expands when subjected to these pressure pulses in the fuel which reduces the magnitude of the pressure pulses and provides a more steady flow of fluid through the pump outlet.
Although the pressure pulse damper of the gerotortype fuel pump disclosed in the noted patent, assigned to the assignee hereof, has enjoyed substantial commercial acceptance and success, improvements remain desirable. One problem with the pressure pulse damper disclosed in the noted patent is the limited durability of the damper as well as the reliability of the device in operation. This pressure pulse damper must be blow molded from a family of plastic materials suitable for blow molding operations which produces considerable scrap material which increases the cost of production. Additionally, blow molded dampers must be carefully designed to obtain a geometry which has an easily compressible portion that flexes, but does not "oil-can", when compressed. To design a durable damper which readily flexes under repeated cyclic loading, special care must be taken to reduce localized stresses which might cause fatigue fractures to the blow molded damper. Therefore, to obtain a damper capable of withstanding full-compression cycle loading, the geometry of the damper becomes critical to minimize fatigue fracturing. Furthermore, the blow-molding operations and assembly process for an annular-shaped damper further increases the final cost of the damper.
Another problem with existing pressure pulse dampers is inadequate reliability and insufficient useful life for the normal life cycle of the fuel pump. The difficulty of designing a blow-molded damper which is sufficiently flexible increases the likelihood that local fatigue fractures will cause a failure of the damper. Likewise, the ability to develop a multi-chamber damping device which is simple to produce, cost effective, and readily made by a blow molding process has proved to be difficult to achieve to date. The reliability and useful life of the current single chamber damper is highly dependent on critical design geometry, the ability to repeatedly achieve full compression without cyclic failure, and stringent control of the wall thickness of the resulting blow molded damper.